The means for sampling the product generally consist in a pump associated with a pushbutton. The pump comprises a central opening. The product enters the opening of the pump, either directly if the container is airless or via a plunger tube extending the pump if the container is non-airless. In both cases, the product enters the pump in a central manner This involves suction, called centralised suction.
This type of central suction has a high suction speed since the product enters the pump directly without pressure loss.
However, there are numerous products that exhibit fragile stability and that can phase change or allow, in the case of a transparent container, a suction stream to occur that is inherent to this type of central suction of the pump at high speed.